The virtualization technology has been one of important functions of an IaaS layer (Infrastructure as a Service). With respect to the virtualization technology, a CPU, memory, I/O, and other devices of a physical machine are virtualized by a virtual machine monitor (VMM) software, a plurality of virtual machines (VMs) are virtualized in one physical machine, and one guest operating system (OS) is operated on each virtual machine. The VMM coordinates with a host operating system (Dom0 or Host OS), to ensure the isolation of the virtual machines located on the same physical machine and online migration of the VM from one physical machine to another physical machine without going down (including the online migration based on shared storage and online migration based on local storage). The virtualization technology has found its wide applications in various large data centers and IaaS platforms in cloud computation environments due to its advantages in VM function and performance isolation, load balancing and system fault tolerance based on VM online migration, application portability, resource utilization rate improvement, operation & maintenance and cost reduction. Its typical applications include high performance computations, big data processing, Web transaction processing, or the like.
In a current cloud storage scheme based on a kernel-based virtual machine (KVM), read and write requests of the virtual machine are directly stored in a host machine locally. When the host machine where the virtual machine is located goes down or the host machine where the virtual machine is located cannot continue a service due to other failures, the virtual machine cannot be recovered quickly since there is no available storage to be accessed by the virtual machine, thereby interrupting the service on the virtual machine.